Click on the stratum key at right for more information about each stratum.
This card provides you with information on the stratigraphy of Site HWK East at Olduvai Gorge. You may get more specific information on each stratum by clicking on that stratum's symbol in the key to the right of the drawing. There is only one profile drawing for this site.
Profile Drawings - HWK East Site Model
This was a thick deposit of reddish-brown to grey tuffs, containing some small clay horizons. The top of the stratum was approximately 30 feet above the level of the base of Bed II. The lower part of the deposit yielded a few artifacts, but these appear to have been intrusive.
This was a thick deposit of reddish-brown to grey tuffs, containing some small clay horizons. The top of the stratum was approximately 30 feet above the level of the base of Bed II. The lower part of the deposit yielded a few artifacts, but these appear to have been intrusive.
This was a thick deposit of reddish-brown to grey tuffs, containing some small clay horizons. The top of the stratum was approximately 30 feet above the level of the base of Bed II. The lower part of the deposit yielded a few artifacts, but these appear to have been intrusive.
This stratum consisted of a re-worked tuff that varied in thickness from 1-2 feet. There were lenses of unconsolidated coarse grey sand that filled hollows in the underlying Sandy Conglomerate stratum. This stratum was designated Level 5, and was only excavated in Trench 3. The stratum yielded 178 artifacts, mostly stone tools. There were some faunal remains, but these were quite few, and very fragmentary.
This illustrates one of the lenses of coarse grey sand that was interbedded with the sandy tuff of Level 5.
This stratum consisted of a cemented, coarse-grained grey sand containing large numbers of artifacts, unmodified cobblestones, and a few broken animal bones. Many of the animal bones showed evidence of having been rolled and abraded by stream action. The upper portion of the stratum was extensively eroded by stream action creating channels with overhanging walls. The deposit was about 2 feet thick. This stratum appears to correlate with the sandy conglomerate stratum noted at Site FLK North. It should be particularly noted that this stratum at this location contained the highest numbers of stone tools made from chert (flint) found anywhere in the Olduvai region. The stratum was designated Level 4 by the excavators.
This stratum was composed of a buff-grey reworked tuff, varying in thickness from 9 inches to 2 feet. There were a few artifacts and bone fragments were scattered through this deposit with an unusually dense concentration of ratifacts and unmodified stone at the bottom of the deposit, at the contact with the underlying stratum. A large number of the artifacts appear to been water-worn, and it is highly likely that most of them were redeposited, or at least partially sorted by stream action. There was a small proportion of chert tools in this level. The deposit was designated Level 3 by the Leakeys.
This was a very thin tuff horizon generally separating Level 2 from Level 3. It was seldom more than a few inches thick and generally occurred in depressions in the surface of Level 2. After checking nearby exposures, where this stratum was more clearly defined, it became apparent that it was the westward equivalent of Tuff IIa. Although a number of samples of this tuff have been analyzed using the K-Ar dating technique, no hard date has been obtained for this tuff. The tuff is heavily reworked everywhere, and is often contaminated with older material. The youngest date obtained (from the least reworked sample) is 1.7 million years which may be close to its true age. Two other samples have yielded dates of 1.76 and 2.1 million years.
This stratum was designated Level 2. It consisted of about 5.5 feet of light brown or buff colored clay containing many root casts. There was a horizontal band of limestone cobbles at a level about 2 feet above the base of the stratum. Although artifacts and faunal remains were scattered throughout the clay, they were more concentrated in two zones, one about half way down the deposit (Upper Level 2), and one near the bottom of the deposit (Lower Level 2). A few of the artifacts were made of chert. The faunal remains in the upper concentration appear to be the carcass of a single animal, probably a rhinoceros. The lower concentration yielded a number of artifacts and manuports (stones brought to the site by hand, but not modified) and was also qute rich in bird remains. This level corresponds with the clay with root casts stratum from Site FLK North.
This was a level zone containing a concentration of limestone cobbles within Level 2. It was located approximately 2 feet above the bottom of the Level 2 deposit.
This was an irregular stratum composed of a coarse-grained grey tuff. in certain portions of the trenches, particularly in Trench 1, the tuff contained rootlets. This deposit is well represented elsewhere in the HWK gullies, and was also found at Site FLK North.
Level 1. This stratum consisted of an irregular horizon of brown silty clay that filled depressions in the upper surface of Marker Tuff If. Marker Tuff If seems to have undergone significant erosion here prior to the deposition of the clay. The occupation floor at this level was remarkable for a number of reasons. First, the unusual pattern of erosion channels cutting through the top of the clay, particularly in Trenches 1 and 2. These channels varied from 2-6 inches deep and 6-12 inches wide. Second, Trench 3 contained a gently curved, raised bank, about 9-10 inches high and averaging 1.5 feet in width. Given the banded distribution of artifacts on either side of this bank, it is possible that the bank served as the base for some sort of shelter or windbreak. There is no indication that the surface of the site was significantly affected by erosion or stream action prior to being buried by the Level 2 clays. Therefore, the distribution pattern of the artifacts may be an indicator of behavioral patterns on the part of the oroginal inhabitants.
Marker Tuff If is the lowest stratum in the sequence at Site HWK East. Seven samples of material from this tuff have been dated (K-Ar), but give very inconsistent results. Two samples date to 1.7 million years. The other five dates, however, range from1.8 to 8.5 million years. Since Tuff If resulted from several different erruptions, it is possible that the older dates reflect inherited argon in the materials of one or more of the eruptions. The two 1.7 million year old dates do accord well with paleomagnetic evidence pertaining to the age of the Olduvai deposits, and probably reflect the actual age of the tuff.